1. Field of the Invention
The present invention relates to a distance-measuring apparatus for measuring the distance to an object to be measured and, more particularly, to an active distance-measuring apparatus suitably used in cameras and other equipment.
2. Related Background Art
The active distance-measuring apparatus used in the cameras etc. is arranged to project light from an infrared-emitting diode (hereinafter referred to as xe2x80x9cIREDxe2x80x9d) toward the measured object, to receive reflected light of the projected light by a position sensing device (hereinafter referred to as xe2x80x9cPSDxe2x80x9d), to process a signal from this PSD by a signal processing circuit and an arithmetic circuit to output distance information, and to determine the distance to the measured object by a CPU. Since the distance measurement with only one projection of light can cause an error, it is desirable that a plurality of light projection operations be carried out to gain a plurality of distance information pieces and that the plurality of distance information pieces be integrated in a fixed period by an integrating circuit to be averaged. The integral of distance information by the integrating circuit is carried out by applying a reference voltage to an integrating capacitor to store charge therein and discharging the capacitor according to the distance information from that state.
The distance-measuring apparatus described above, however, has the problem of long distance measurement time. For example, where the integral of distance information is carried out by charge and discharge of the integrating capacitor, the charge and discharge time varies with change in the number of emissions depending upon the distance measurement condition such as the luminance or the like. Therefore, in the step of distance measurement the charge and discharge time needs to be set to the maximum time when the charge and discharge time becomes maximum. This setting to the maximum time, however, requires a lapse of the maximum time equally as the charge and discharge time even in cases wherein the charge and discharge time is short. Therefore, it requires unnecessarily long measurement time.
Therefore, the present invention has been accomplished in order to solve this problem and an object of the present invention is to provide a distance-measuring apparatus that can measure the distance within a reduced measurement time.
A distance-measuring apparatus according to the present invention is a distance-measuring apparatus comprising: light projecting means for projecting pulses of light toward a measured object; light receiving means for receiving reflected light of the light projected toward the measured object, at a photoreceptive position on a position sensing device according to a distance to the measured object and outputting a signal according to the photoreceptive position; arithmetic means for carrying out an arithmetic operation based on the signal outputted from the light receiving means and outputting an output ratio signal according to the distance to the measured object; integrating means comprising an integrating capacitor, the integrating means carrying out a first integral in which the signal outputted from the arithmetic means is integrated by discharging/charging the integrating capacitor according to the signal outputted from the arithmetic means and thereafter carrying out a second integral by charging/discharging the integrating capacitor at a constant current, the integrating means comparing a voltage of the integrating capacitor with a reference voltage during the second integral and outputting a comparison result signal according to a result of the comparison; maximum second integral time selecting means for selecting one of a plurality of maximum second integral times, each being set as a process time of the second integral, according to a distance measurement condition; and detecting means for detecting the distance to the measured object, based on the signal outputted from the integrating means, after a lapse of the maximum second integral time.
The distance-measuring apparatus according to the present invention is also characterized in that the maximum second integral time selecting means selects the maximum second integral time according to the distance measurement condition of one of luminance, ambient temperature, and focal length.
According to the present invention, the maximum second integral time is properly set according to the distance measurement condition and the next operation is carried out after a lapse of the maximum second integral time. Therefore, the next operation can be carried out soon after completion of the second integral, thus reducing the distance measurement time.
The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.